1. Field of the Invention
This invention pertains to apparatus for the separation of the components of fluid mixtures employing permselective membranes. More particularly, this invention is directed to apparatus useful in reverse osmosis, ultratiltration, electrofiltration, and gaseous separation processes, said apparatus featuring a porous body as membrane support and a pressure-tight shell encasing the body and membrane with means for feeding to and withdrawing from the interior of the shell.
The components of fluid mixtures are separated in this apparatus by means of a membrane selectively more permeable to some components of the mixture than to other components by bringing the mixture into contact with the membrane under pressure. The components which pass through the membrane and a mixture depleted in these components are then collected from the two sides of the membrane.
2. Prior Art
Many different forms of apparatus have been designed for separating the components of fluid mixtures by means of pressure and a selectively permeable membrane. All contain a suitable membrane, means for introducing a feed mixture to be separated, means for contacting this mixture with one surface of the membrane, means for maintaining the feed mixture under pressure, means for removing a mixture depleted in the more permeable components from the contacted surface of the membrane, and means for recovering the more permeable components which pass through the membrane.
In such apparatus, the rate at which the more permeable components of the feed mixture passes through the membrane is directly related to the permeability of the membrane for these components, the area of the membrane, and the effective operating pressure. Improvements in membrane permeability, in membrane area per unit volume, and in the tolerance for higher operating pressures and temperatures have been sought in various ways. For example, increased membrane permeability has been obtained through the use of thin membranes formed on, adherent to, and partially integral with porous supports.
In apparatus employing membranes supported by porous structures, greater efficiency at a given operating pressure can generally be obtained by increasing the permeability of the support material. However, increased permeability is usually accompanied by some reduction in strength. Efficiency at a given operating pressure can also be increased by reducing the length of the permeate flow path through the porous structure, such as by use of thin porous structures.
The porous supports for selectively permeable membranes, and particularly tubular, plate-like, and odd-shaped supports, have been used in many combinations and permutations in various devices. Such as those disclosed in U.S. Pat. No. 3,156,654 and U.S. Pat. No. 3,400,825.
A more recent device is shown in U.S. Pat. No. 3,598,241 which describes a body of a porous material with multiple passages therethrough and with membranes on the surfaces of the passages. This body is connected to means for introducing a feed solution into the passages and for removing a concentrated solution from the passages. A trough provides a means for collecting liquids passing through the membrane and dripping from the outsides of the porous body. Such a device requires that the porous body be relatively thick in smallest section to withstand the high pressures which are desirable in separations involving permselective membranes. The necessity for thick sections will limit the practical amount of membrane surface per unit volume in separation apparatus incorporating this concept, and lead to more weight of porous material and larger apparatus which in turn leads to higher cost than would be required with better membrane area to unit volume ratios.
It is an object of this invention to provide a separatory device having a high ratio of membrane area to device volume in which the membrane is supported by a porous body. It is a further object of this invention to provide such a device capable of operating at high pressure. These and other objects are obtained by this invention as described and illustrated hereinafter.